Scientists had assumed the three-foot ice was too thick to allow for the growth of plants, but according to Nasa scientists four times more of the phytoplankton was found under the ice than in nearby ice-free water.

Nasa said the waters were "richer in microscopic marine plants, essential to all sea life, than any other ocean region on Earth".

Phytoplankton is thought to be responsible for about as much oxygen as all of the land plants on Earth - but was only discovered in the 1970s.

The Icescape (Impacts of Climate on EcoSystems and Chemistry of the Arctic Pacific Environment) mission was sponsored by Nasa, and the publication of its findings will give clues about how the phytoplankton impacts on the environment.

"The finding reveals a new consequence of the Arctic's warming climate and provides an important clue to understanding the impacts of a changing climate and environment on the Arctic Ocean and its ecology," Nasa said.